During and after the Gulf War, people reported that they had
been exposed to chemical warfare agents. To investigate these
incidents and to determine if chemical weapons were used, the DOD
developed a methodology for investigation and validation based on
work done by the United Nations and the international community
where the criteria include:

A detailed written record of the conditions at the
site.

Physical evidence from the site such as weapons
fragments, soil, water, vegetation or human/animal
tissue samples.

A record of the chain of custody during
transportation of the evidence.

Testimony of eyewitnesses.

Multiple analyses.

Review of the evidence by experts.

While the DOD methodology (Tab
D) for investigating chemical incidents is based on these
protocols, the passage of time since the Gulf War makes it
difficult to obtain certain types of documentary evidence, and
physical evidence was often not collected at the time of an
event. Accordingly, our methodology is designed to provide a
thorough, investigative process to define the circumstances of
each incident and determine what happened. Alarms alone are not
considered to be certain evidence of chemical agent presence, nor
is a single individuals observation sufficient to validate
a chemical agent presence.

By following our methodology and accumulating anecdotal,
documentary, and physical evidence, and by interviewing
eyewitnesses and key personnel, and analyzing the results, the
investigator can assess the validity of the presence of chemical
warfare agents on the battlefield. Because information from
various sources may be contradictory, we have developed an
assessment scale (Figure 1) ranging from "Definitely"
to "Definitely Not" with intermediate assessments of
"Likely," "Unlikely," and
"Indeterminate." This assessment is tentative, based on
facts available as of the date of the report publication; each
case is reassessed over time based on new information and
feedback.

Figure 1. Assessment of Chemical Warfare Agent
Presence

The standard for making the assessment is based on common
sense: do the available facts lead a reasonable person to
conclude that chemical warfare agents were or were not present?
When insufficient information is available, the assessment is
"Indeterminate" until more evidence can be found.